Deep Dive: E4C04
The correct answer is D: The ratio in dB of the noise generated by the receiver to the theoretical minimum noise. What is the noise figure of a receiver is the ratio in dB of the noise generated by the receiver to the theoretical minimum noise. Noise figure compares receiver noise to ideal (thermal) noise. For amateur radio operators, this is important for receiver performance. Understanding this helps when evaluating receivers.
Why Other Answers Are Wrong
Option A: Incorrect. Ratio of atmospheric noise to phase noise isn't noise figure - noise figure is receiver noise vs theoretical minimum. Atmospheric/phase noise isn't noise figure. Option B: Incorrect. Ratio of noise bandwidth to theoretical bandwidth isn't noise figure - noise figure is receiver noise vs theoretical minimum. Bandwidth ratio isn't noise figure. Option C: Incorrect. Ratio of receiver noise to atmospheric noise isn't noise figure - noise figure is receiver noise vs theoretical minimum. Atmospheric noise isn't the reference.
Exam Tip
Noise figure = ratio in dB of receiver noise to theoretical minimum noise. Think 'N'oise 'F'igure = 'N'oise 'F'rom receiver vs 'I'deal. Noise figure compares receiver noise to ideal (thermal) noise. Not atmospheric/phase noise, not bandwidth ratio, not atmospheric noise - just receiver noise vs theoretical minimum.
Memory Aid
Noise figure = ratio in dB of receiver noise to theoretical minimum noise. Think 'N'oise 'F'igure = 'R'eceiver vs 'I'deal. Noise figure compares receiver noise to ideal (thermal) noise. Important for receiver performance.
Real-World Example
The noise figure of a receiver: It's the ratio in dB of the noise generated by the receiver to the theoretical minimum noise (thermal noise). A perfect receiver would have 0 dB noise figure. Real receivers have higher noise figures. This is what noise figure is - receiver noise vs theoretical minimum.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E4C
Reference: 2024-2028 Question Pool · E4 - Amateur Practices
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E4C topic.